In the United States, degenerative arthritis of the thumb carpometacarpal (CMC) joint affects up to 8% of men and 25% of women ages 50 and older. The impact of this disease on U.S. healthcare expenditures is predicted to increase substantially as the population of people ages 60 and older doubles by 2050. Studies on the surgical treatment options of this disease have shown comparable outcomes on symptom relief, preservation of function, and patient satisfaction. However, the lack of comparative effectiveness studies to provide an evidence-based treatment approach of this disease leads to unnecessary variations in treatment and misappropriation of healthcare resources. Numerous studies in the literature have been limited to case series relating to surgeon experiences. Consequently, no inferences can be made on how variations in surgical treatment manifest at the population level. Additionally, studies do not adequately evaluate how patient and health system factors influence these variations. We hypothesize that patient factors and geographic location contribute greatly to the variation in patterns of surgical treatment of thumb CMC arthritis. We thus propose to use national Medicare claims data to retrospectively evaluate the national variation in patterns of use and expenditures of different surgical techniques in the treatment of thumb CMC arthritis. Furthermore, we aim to evaluate the complication rates associated with these treatment options to calculate the additional costs incurred. The results from this proposed study will highlight the need for comparative effectiveness studies in the treatment of this disease and, ultimately, identify cost- effective, low-morbidity treatment option in order to better guide physicians and patients in the treatment of thumb CMC arthritis.